[Intel-gfx] [Mesa-dev] [PATCH] i965: Revert absolute mode for constant buffer pointers.

[Kenneth Graunke]

On Wednesday, October 25, 2017 7:33:41 AM PDT Jason Ekstrand wrote:
> On October 25, 2017 06:05:16 Joonas Lahtinen wrote:
[snip]
> > There indeed seems to be quite a lot of missing registers from the i915
> > driver where the context is initialized. (Psst. You can read that as:
> > "all the 33 non-privileged registers we could quickly list, are
> > missing").
> 
> We probably don't need *all* of them initialized.  For instance, the 
> initial values of the ALU registers or the indirect draw parameter 
> registers will probably never matter.  However, if you want to just 
> initialized them all, that's fine.

I agree - I think we can cut down the list substantially, if you like.
Here's my breakdown of Skylake's non-privileged register list:

Cache_Mode_0               0x7000
Cache_Mode_1               0x7004
GT_MODE                    0x7008
L3_Config                  0x7034
TD_CTL                     0xE400
TD_CTL2                    0xE404
L3SQCREG4                  0xB118
NOPID                      0x2094
INSTPM                     0x20C0

   Should be initialized by the kernel.  Several of these can severely
   break unsuspecting userspace, and we'd like to be able to rely on a
   default value.

IA_VERTICES_COUNT          0x2310
IA_PRIMITIVES_COUNT        0x2318
VS_INVOCATION_COUNT        0x2320
HS_INVOCATION_COUNT        0x2300
DS_INVOCATION_COUNT        0x2308
GS_INVOCATION_COUNT        0x2328
GS_PRIMITIVES_COUNT        0x2330
SO_NUM_PRIMS_WRITTEN0      0x5200
SO_NUM_PRIMS_WRITTEN1      0x5208
SO_NUM_PRIMS_WRITTEN2      0x5210
SO_NUM_PRIMS_WRITTEN3      0x5218
SO_PRIM_STORAGE_NEEDED0    0x5240
SO_PRIM_STORAGE_NEEDED1    0x5248
SO_PRIM_STORAGE_NEEDED2    0x5250
SO_PRIM_STORAGE_NEEDED3    0x5258
CL_INVOCATION_COUNT        0x2338
CL_PRIMITIVES_COUNT        0x2340
PS_INVOCATION_COUNT_0      0x22C8
PS_DEPTH_COUNT_0           0x22D8
PS_INVOCATION_COUNT_1      0x22F0
PS_DEPTH_COUNT_1           0x22F8
PS_INVOCATION_COUNT_2      0x2448
PS_DEPTH_COUNT_2           0x2450
GPGPU_THREADS_DISPATCHED   0x2290

   The kernel can skip these if you like.  Statistics registers just count
   things, and userspace always calculates (end counter - start counter)
   deltas, so the initial value doesn't really matter.

SO_WRITE_OFFSET0           0x5280
SO_WRITE_OFFSET1           0x5284
SO_WRITE_OFFSET2           0x5288
SO_WRITE_OFFSET3           0x528C
GPUGPU_DISPATCHDIMX        0x2500
GPUGPU_DISPATCHDIMY        0x2504
GPUGPU_DISPATCHDIMZ        0x2508
MI_PREDICATE_SRC0          0x2400
MI_PREDICATE_SRC0          0x2404
MI_PREDICATE_SRC1          0x2408
MI_PREDICATE_SRC1          0x240C
MI_PREDICATE_DATA          0x2410
MI_PREDICATE_DATA          0x2414
MI_PREDICATE_RESULT        0x2418
MI_PREDICATE_RESULT_1      0x241C
MI_PREDICATE_RESULT_2      0x23BC
3DPRIM_END_OFFSET          0x2420
3DPRIM_START_VERTEX        0x2430
3DPRIM_VERTEX_COUNT        0x2434
3DPRIM_INSTANCE_COUNT      0x2438
3DPRIM_START_INSTANCE      0x243C
3DPRIM_BASE_VERTEX         0x2440

   The kernel can skip these if you like, IMO.  These registers are only
   used when enabling an optional feature - stream out (SO_WRITE_*),
   indirect compute dispatch (GPGPU_*), predicated draws (MI_PREDICATE_*),
   indirect draws (3DPRIM_*).  Userspace has to explicitly opt in to each
   of these features by enabling a flag, so there isn't a cross-context
   contamination problem.  If userspace opts in to these features, it can
   be responsible for programming the registers correctly.

CS_GPR (1-16)              0x2600

   The kernel can skip these if you like.  They're temporary storage when
   using the MI_MATH instruction.  Example usage: load values into CS_GPR1
   and CS_GPR2, add them, store the result in CS_GPR3.  Store to memory.

   Nobody should be doing math on register values without setting them.
   That's clearly a userspace bug.

BB_OFFSET                  0x2158
OA_CTX_CONTROL             0x2360
OACTXID                    0x2364
OA CONTROL                 0x2B00
PERF_CNT_1_DW0             0x91b8
PERF_CNT_1_DW1             0x91bc
PERF_CNT_2_DW0             0x91c0
PERF_CNT_2_DW1             0x91c4

   I don't know about these.
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